1. Field of the Invention
The present invention relates to an image sensing device that includes an image sensor having both an array of electron emission sources and a photoelectric conversion film and a drive circuit that drives the image sensor.
2. Description of the Related Art
An image sensing device, which includes an image sensor having an array of electron emission sources arranged in a matrix, each outputting electrons through application of an electric field, and a photoelectric conversion film, has been proposed. For example, a High-efficiency Electron Emission Device (HEED) has been proposed as an electron emission source (specifically, as a cold cathode electron source) (for example, see Pioneer R&D, Vol. 17, No. 2, 2007, pp. 61-69).
The HEED enables low-voltage driving and features a simple structure, and studies are underway on application of HEEDs to image sensing devices. An example of the photoelectric conversion film is a High-gain Avalanche Rushing amorphous Photoconductor (HARP).
However, if a very bright image is incident on the photoelectric conversion film, an excessively large amount of hole charge is accumulated in one pixel area of the photoelectric conversion film, and the amount of electrons emitted by the electron emission source is insufficient to neutralize the accumulated holes, causing a problem of detected signal saturation when image information is read.
In addition, due to defective pixels of the cold cathode array, there is a problem, for example in that there is a pixel which cannot detect (or reproduce) an image signal since no or almost no electrons are emitted from the pixel or there is a pixel which causes signal saturation even though the brightness of incident light is normal since the amount of emitted electrons is less than a criterion value or a required value.
Such a defective pixel always becomes a black dot, which is obtrusive noise in terms of image quality. Thus, in the related art, a processor provided downstream for processing the reproduced signal performs so-called signal interpolation. That is, the processor calculates an average of the reproduced signals of left and right pixels or top, bottom, left, and right pixels and replaces the reproduced signal of the black-dot pixel with the average. However, in the related art, a pixel for interpolation is specified from the reproduced image and thus there is a problem in that it is difficult to determine whether the reason why the pixel is black is that the sensed image is black or that the pixel is defective. In addition, there is a problem in that correction is not performed on a pixel that suddenly becomes defective during use.